It's been many years, but I have been to a party where I came home without my shoes. Actually, the party was in the house where I lived, but somehow my favorite Top-siders were gone as the fog cleared the next day, and were never seen again. That, evidently, was a pretty good party.
But I think the poster of this sign has one over on me.
The sign is posted where the bike trail meets the parking lot of a newish and very nice hotel, so it's not entirely clear where the individual was parted from his/her shoe and leg brace. My first thought was of a rustic soiree along the river, but perhaps it was an indoor occasion, where the evening's dancing required one to be unencumbered by footwear -- or, in this case, half of one's footwear.
To make things more interesting, there's no getting around the fact that the sign implies the two missing items are a united pair. To me, the sign quite clearly does not say, "I lost my shoe, dammit. And, come to think of it, I have also lost, quite by coincidence, a leg brace."
No, to me the sign says, "I lost my shoe/leg brace combination. No room here to explain, but I really, really need it back."
All of this leads me to the conclusion that the lost item is basically a prosthesis. And while losing one has got to be a huge downer, the circumstances under which this would happen could well make you the envy of partiers everywhere.